1. Osteoporosis is "a pediatric disease with geriatric consequences". Simply stated, suboptimal skeletal. 2. Development in childhood and adolescence may result in decreased bone strength and an increase in lifetime 3 fracture incidence. A delay in the onset of puberty (primary amenorrhea) correlates with both low bone mass;4. and an increased incidence of stress fracture. Suboptimal bone accrual may have long term consequences. 5. Even with current treatment options as studies that treated amenorrheic dancers for 2 years with hormone 6 replacement therapy found no difference in bone mineral density between treated and placebo groups. The 7 most significant factors during development may be nutritional and lifestyle factors. Therefore, our overall goal 8 is to ascertain the affect of delayed pubertal development on the mechanism of bone loss at maturity. 9 Density measures alone, although widely used clinically, cannot identify osteoporotic subjects who will sustain 10 fractures, due to the large overlap in bone mass measures in individuals with fractures and those without 11 fractures. Other factors including bone size, architecture and material properties must be considered. We 12 have recently developed a texture analysis approach using Gabor filters, which is capable of providing insight 13 into bone structure from localized texture information on a pixel level. The texture approach is therefore a 14 potentially powerful tool in analyzing trabecular bone texture where orientation, shape and architecture as well 15 as density are the fundamental components. Our previous work was analyzing 2D images but we propose to 16 transfers this approach to 3D images. This novel approach will indicate not only bone mass changes but 17 changes in orientation which may be very significant later in life. In Aim #1, We will test the hypothesis that 18 the mechanism and magnitude of bone loss in a mature animal is dependent on bone development. 19 Specifically, delayed pubertal onset will alter the architecture of bone that will affect the mechanism of 20 bone loss at maturity. Pubertal delay will be completed by gonadotropin releasing hormone antagonist 21 (GnRH-antagonist) injections. At 50 days of age changes in bone morphology will be evaluated using a novel 22 3D texture analysis. The following biomarkers will be measured to assess the response of pubertal delay on 23 systemic changes in bone metabolism osteocalcin (a marker of bone formation) and N-telopeptide of collagen 24 type I (NTx) (a marker of bone resorption). Serum estradiol and IGF-1 will also be assayed to confirm the 25 hormonal response to the protocol. Flourescent histomorphometry will assess bone formation rates on 26 trabecular bone. At maturity (150 days of age) the experimental rats will undergo ovariectomy surgery to 27 model post menopausal bone loss. Changes in bone morphology will be evaluated using static and dynamic 28 histomorphometry, micro-CT and texture analysis. By using a systems approach relating environmentally 29 induced delayed puberty to bone growth, we propose to gain a new understanding of the important relationship 30 between growth and its variability and the bone structure we become heir to during the aging process 31. PUBLIC HEALTH RELEVANCE: Fracture risk in the elderly has its origins during growth and development. A delay in the onset of puberty results in both low bone mass and an increased incidence of stress fracture in young women. Therefore, the failure to accrue peak bone mass during the adolescent years represents a missed opportunity to optimize bone mass during one's life.